Spinal motoneuron function in lower motor neuron disease: normal corticomotoneuronal and peripheral Ia EPSPs in patients with spinal muscular atrophy.

Responses of single tibialis anterior motor units to transcranial magnetic stimulation and to a synchronized Ia volley evoked by peripheral electrical nerve stimulation were obtained in patients with distal spinal muscular atrophy and compared to normal controls. Estimations of excitatory postsynaptic potential (EPSPs) by cross-correlations revealed no difference in rise time of EPSPs for both groups of subjects despite considerable changes in macro-EMG parameters of the motor units studied in patients with spinal muscular atrophy (SMA). The results indicate that voluntarily activated spinal motoneurons in SMA are capable of normal excitatory responses to transcranial magnetic as well as peripheral Ia stimulation.